The objective of this proposal is to develop a fund of knowledge describing the pharmacologic interactions between herbal products and standard asthma medications. We hypothesize that herbal medicines may alter the pharmacokinetics (i.e., the absorption, distribution, and metabolism) of some asthma medications and therefore the patient's clinical response to these drugs. However, because herbal products are exempt from FDA regulations, the information necessary to predict such interactions is generally unavailable. Studies will be conducted to systematically investigate potential herb-drug interactions in highly standardized experiments using reagents typically used by pharmaceutical companies in development of new drugs. Herbal products will be evaluated in vitro for their ability to inhibit drug metabolizing enzymes using recombinant cytochrome P-450 enzymes. In addition, herbal products will be evaluated for their ability to induce drug metabolizing enzymes in vitro using cultured human hepatocytes. When potential herb-drug interactions are identified by in vitro studies, their clinical significance will be evaluated in pharmacokinetic studies with human volunteers in a future proposal. The results from our studies will be published in the scientific literature and also on the website of the UC Davis Center for Complementary and Alternative Medicine Research in Asthma and Allergy. This information can be used by patients and physicians who wish to use both herbs and standard medications more safely by the FDA to formulate policy, and by pharmaceutical companies to predict potential interactions with their products already on the market or with drugs under development.